Cite? I have seen nothing from the Australian authorities saying that the reason for this move is specifically because they believe vaccines are ineffective at reducing transmission.
There are concerns that some vaccines are less effective at all against certain mutant strains. And the virus is obviously still rampant in many parts of the world, so the Australian move is perfectly understandable. But there is a growing body of evidence that, in accord with expectation, vaccines that are effective against preventing disease are also effective at preventing transmission.
Discussed in the other thread here and subsequent posts.